Some specimens of Cherty rock forwarded to England for determination some years since by Mr. H. Y. L. Brown, F.G.S., Government Geologist of South Australia, have lately been submitted to me for examination by my friend Dr. H. Woodward, F.R.S., and their structure, as shown in thin sections, seems to me sufficiently interesting to be recorded. The specimens in question are of a light or yellowish-grey tint, with a waxy lustre, in some portions compact and in others minutely porous, which makes them light to the feel. The rock is hard, scratching glass readily, and there is no reaction with acid.